This proposal requests the support for the purchase of a time correlated nanosecond fluorescence spectrometer with the capacity to measure the decay of fluorescence intensity and anisotropy as an explicit function of time on the x-axis. Professor Berman proposes to employ nanosecond polarization measurement to examine the segmental flexibility of the asymmetrical molecular forms of acetylcholinesterase derived from Torpedo californica. This protein assembly is suitable for spectroscopic study by virtue of the availability of high concentrations of the different molecular forms of AchE purified to homogeneity, as well as site specific fluorescence probes which bind in a stoichiometric manner and exhibit a wide range of fluorescence lifetimes out to 200nsec. Professor Jung proposes to examine the spatial dimensions of the Band 4.5 protein (glucose transport protein of the red cell) employing resonance excitation transfer and would require the capacity to ascertain the extent of dynamic quenching through independent measurement of the respective lifetime components. Professor Yeagle proposes to examine the interaction between a novel fluorescent sterol derivative, dehydroergosterol, and membrane proteins employing time correlated anisotropy decay. The capacity to measure responses over the nanosecond time domain as well as resolve the amplitudes and decay times of the contributing components represents an essential requirement of these studies.